The vote - which specifically stated that the drug's risk does not outweigh its benefit - is non-binding, but the agency's regulatory authorities usually take the advice of the advisors. The FDA is expected to make a formal decision on the drug in July.

Zimulti is already available in 10 European countries, as well as several other nations including Mexico. But the FDA published documents earlier this week acknowledging that the drug increased depression and suicidal thoughts in patients.

"That was a primary concern, so we're not surprised [by the vote,]" said Aileen Salares, analyst for Leerink Swann. "It's obvious that the FDA is looking very closely at side effects."

FDA commissioner Andrew von Eschenbach was grilled at a Congressional hearing last week for failing to detect a heightened risk heart attacks that have been blamed on GlaxoSmithKline's (up $0.33 to $52.37, Charts) Avandia and Merck's (up $0.45 to $50.67, Charts, Fortune 500) Vioxx, drugs that were both approved by the agency. Merck took Vioxx, an arthritis painkiller, off the market in 2004 and about 27,000 lawsuits have been filed against the company. The FDA is expected to impose a "black box," the most severe type of warning, on Avandia, which remains on the market.

Some analysts have pegged Zimulti as a potential blockbuster because it has been studied for so many potential uses, including diabetes treatment and smoking cessation. But even prior to Wednesday's vote, analysts considered the drug risky because of its problems in trying to make it past the FDA. In 2006, when Sanofi (down $1.31 to $43.07, Charts) was trying to get the drug approved for smoking cessation, the FDA sent the company an "approvable letter," meaning that it needed to run more tests before getting a green light.

Diet drugs make up a small part of the $40 billion weight loss industry. If Zimulti does get approved, it would compete with Abbott's (up $0.85 to $54.19, Charts, Fortune 500) Meridia, which totaled $345 million in 2006 sales, and Roche's over-the-counter Xenical. Companies generally do not break out sales for OTC drugs, which typically pale in comparison to prescription.

Salares does not own Sanofi stock. Leerink Swann does not do business with the company and does not cover it specifically.